With respect to the question at 30:22 Why do we see Cosmic Microwave Background (CMB) from all directions continuously, and why it does not pass us by just in an instant: There is some part of universe which is exactly as far from earth when CMB originated from that part is reaching on earth just now. Such elements in universe are in all directions from earth. Remember that CMB was emitted 380,000 years ago from each and every part of universe. As soon as CMB from that part finishes, another adjacent part opens whose CMB is just reaching now. And thus the process continues. Since every part of universe emitted CMB, we will never run out of some area of universe whose CMB has not reached earth yet, and will keep on progressively reaching us. And this process will never end as universe is still expanding. So we will see CMB from some part of universe in all directions till universe is expanding. However as the CMB that is reaching earth is now coming from areas that are moving away from earth faster and further, the received CMB frequency will keep decreasing on account of Doppler Effect. A point will be come when that frequency will become zero. At that point, the regions emitting CMB will not manage to have to those waves reach earth, and CMB reception on earth will stop.
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With respect to the question at 30:22
Why do we see Cosmic Microwave Background (CMB) from all directions continuously, and why it does not pass us by just in an instant:
There is some part of universe which is exactly as far from earth when CMB originated from that part is reaching on earth just now. Such elements in universe are in all directions from earth. Remember that CMB was emitted 380,000 years ago from each and every part of universe.
As soon as CMB from that part finishes, another adjacent part opens whose CMB is just reaching now. And thus the process continues.
Since every part of universe emitted CMB, we will never run out of some area of universe whose CMB has not reached earth yet, and will keep on progressively reaching us. And this process will never end as universe is still expanding. So we will see CMB from some part of universe in all directions till universe is expanding.
However as the CMB that is reaching earth is now coming from areas that are moving away from earth faster and further, the received CMB frequency will keep decreasing on account of Doppler Effect. A point will be come when that frequency will become zero. At that point, the regions emitting CMB will not manage to have to those waves reach earth, and CMB reception on earth will stop.
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